The present invention relates to communication systems, and in particular, to techniques for performing blind channel estimation.
FIG. 1 illustrates a communication system including a transmitting system 101 (“transmitter”) and a receiving system 103 (“receiver”). The transmitter transmits a signal including information across a communication channel 102 to the receiver. Each of the transmitting system 101 and the receiving system 103 may include both a transmitter and receiver for sending and receiving signals across the communication channel 102.
Communication channels are often characterized by impulse response, or equivalently, frequency response. For example, if a signal is transmitted across the communication channel, the signal may be modified as a result of having propagated through the communication channel. Since it is typically desirable to receive the same signal at the output of the communication channel as was transmitted at the input of the communication channel, such changes or modifications to the signal are referred to as distortion. Distortion may include attenuation of certain frequency components or phase shifting of such frequency components, for example. Causes of distortion may include inter symbol interference, reflections, or non-idealities of the communication channel. The impulse response (or frequency response) may be used to model the distortion of a communication channel. The receiver may reduce the distortion of the received signal in order to obtain a more accurate representation of the transmitted signal. For discrete time signal processing, the impulse response and frequency response may be represented as discrete time or frequency functions. In FIG. 1, the communication channel 102 is represented by a discrete time impulse response h(n).
In some communication systems, information having predefined characteristics may be sent across the communication channel to measure the effects of the communication channel on the transmitted signal. The impulse response of the communication channel may then be determined by examining the actual effects of the channel on the transmitted and received signal, where the transmitted signal is known (e.g., the transmitted signal contains known characteristics, for example, in a preamble). One problem with this technique is that the communication systems must execute a calibration or training sequence by sending and receiving the predefined information. In many communication systems, it is desirable to receive the transmitted signal and estimate the impulse response from the properties of the received signal. If an accurate estimate of the impulse response can be obtained, the receiver may be configured to correct for some of the distortion of the channel. Existing techniques for estimating the impulse/frequency response of a communication channel are computationally intensive, lack desired accuracy, and/or suffer from other problems.